Generator sizing Last reviewed June 2026

Generator Propane Consumption Calculator + Runtime Chart

By the WhatSize editorial team 5 min read Standards-reviewed

TL;DR

A 7,500-watt generator running at 50% load burns 0.8-1.2 gallons of propane per hour. On a standard 20-lb BBQ tank (4.7 gallons), that's about 4-6 hours. On a 100-lb tank (23.5 gallons), you get 20-30 hours of runtime at 50% load.

Looking for a different size? See What Size Generator for a 2,000 Sq Ft House? or browse all generator sizing guides.

Propane vs Gasoline: Fuel Economics for Generator Backup

Propane is the preferred fuel for standby generators because it doesn't degrade in storage (gasoline goes bad in 3-6 months) and produces fewer engine deposits. The tradeoff is energy density: propane contains about 91,500 BTU per gallon vs gasoline's 114,000 BTU, so you need more fuel volume for the same runtime.

Fuel consumption depends primarily on load level, not generator size. A generator at 25% load uses roughly 30-40% less fuel than at 75% load. For budgeting, assume 50% load (the most efficient operating point for fuel-to-electricity conversion).

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DuroStar DS13000MX 13,000W Dual Fuel #ad

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Dual Fuel (Gas/Propane)13,000W PeakElectric Start

$899 approx

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MID-RANGE

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Amazon

These Amazon-available picks meet the calculated spec. For region-specific or licensed contractor-installed options, consult a local professional. See our Disclaimers.

Propane Consumption by Generator Size and Load

5,000W generator at 50% load: ~0.6 gal/hr — 20-lb tank lasts ~8 hours, 100-lb tank ~39 hours
7,500W generator at 50% load: ~1.0 gal/hr — 20-lb tank ~5 hours, 100-lb tank ~24 hours
12,000W generator at 50% load: ~1.5 gal/hr — 20-lb tank ~3 hours, 100-lb tank ~16 hours
22,000W standby at 50% load: ~2.8 gal/hr — requires a 250-gallon tank for multi-day outages

Frequently asked questions

How long will a generator run on a 20-lb propane tank?

At 50% load, a 5,000W generator runs about 8 hours on a 20-lb tank. A 7,500W runs about 5 hours. A 12,000W runs about 3 hours. Always keep at least 2 spare tanks for storms.

Is propane or gasoline better for generators?

Propane: longer shelf life (indefinite), cleaner burning, lower maintenance. Gasoline: higher energy density, easier refueling during outages. Dual-fuel generators let you choose based on availability.

How much propane does a whole-house generator use per day?

A 22kW standby generator burns about 2.8 gal/hr at 50% load or roughly 67 gallons per day. A 500-gallon tank provides about 7 days of continuous operation. For multi-day outages, schedule off-hours to conserve fuel.